Method for determining the air entering the cylinders of an internal combustion engine having a supercharger

ABSTRACT

A device for determining air entering cylinders of an internal combustion engine having a supercharger. The air is determined as a function of such quantities as rpm, air throughput in the intake manifold, throttle valve position values and temperature, characterized in that at least the following physical relationships are included in the determination: 
     suction equation of the engine 
     balancing equation for a filling in an intake manifold 
     flow rate equation at a throttle valve 
     balancing equation in a volume between the throttle valve and the supercharger.

FIELD OF THE INVENTION

The present invention relates to a method for determining the airentering the cylinders of an internal combustion engine having asupercharger.

BACKGROUND INFORMATION

German Patent No. 32 38 190 describes an “Electronic System forControlling or Regulating Performance Characteristics of an InternalCombustion Engine.” Specifically, it describes a method of determiningthe pressure in the intake manifold on the basis of the rpm and the airflow rate in the intake manifold and conversely the air flow rate on thebasis of the rpm and pressure. The method described therein makes usespecifically of physical relationships prevailing in the air intakemanifold with the goal of optimal control of the internal combustionengine.

International Patent Publication No. WO96/32579 describes a method ofmodel-supported determination of the air entering the cylinders of aninternal combustion engine. To do so, a physical model is crated,describing the relationships in the intake system of an internalcombustion engine without a supercharger, using parameters representingthe degree of opening of the throttle valve, the ambient pressure andthe valve position as input quantities of the model. In addition, theinstantaneous value determined for the air entering the cylinders of theinternal combustion engine is used to predict future values.

The conventional system cannot be used with supercharged internalcombustion engines, because additional physical factors must also betaken into account due to the supercharging.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a device fordetermining the air entering the cylinders of an internal combustionengine having a supercharger as a function of quantities such as rpm,air throughput in the intake manifold, throttle valve position valuesand temperature which comprehensively take into account the physicalprocesses taking place in supercharged internal combustion engines.

With this device according to the present invention, it is possible todetermine the physically correct or at least approximate relationshipsprevailing in the intake manifold of an internal combustion enginehaving a supercharger, and then to base the determination of thequantity of fuel accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a survey diagram of an internal combustion engine having asupercharger.

FIG. 2 shows a block diagram of a determination of a relative fillingper stroke on a basis of standardized quantities for a throttle valveangle, temperature of an intake air upstream from the throttle valve, amass flow over a hot film air flow meter and an rpm.

FIG. 3 shows a block diagram for calculation of a mass flow over athrottle valve.

DETAILED DESCRIPTION

FIG. 1 shows in a rough survey diagram the input side of an internalcombustion engine having a supercharger. As seen in the direction offlow, the air intake manifold includes a hot film air flow meter 10(HFM), a supercharger or compressor 11, a throttle valve 12 and anintake valve 13 of internal combustion engine 14. One volume 16 betweensupercharger 11 and the throttle valve and an additional volume 17between the throttle valve and intake valve 13 are also important for anunderstanding of the present invention. The internal combustion engineitself has a piston 18 for each cylinder, with the low position of thepiston characterizing piston displacement 19.

FIG. 1 shows that the relationships in the intake manifold can becharacterized by

a suction equation for the internal combustion engine (air flow throughintake valve 13),

a balancing equation for the filling in the intake manifold between thethrottle valve and the intake valve (volume 17),

a flow equation at throttle valve 12 and

a balancing equation in volume 16 between supercharger 11 and throttlevalve 12.

The equations are based on a two-mass storage model, with the two massstorages indicating the volumes upstream and downstream from thethrottle valve (16, 17).

It has proven expedient to use standardized values for the equations.

In particular, the goal is to assume mass contents ml in volume 16upstream from throttle valve 12 and ms in volume vs 17 downstream fromthe throttle valve, to convert the mass contents into pressures upstreamand downstream from the throttle valve and to determine on the basis ofthese two pressures mass flows which in turn permit updating of the masscontents. The individual calculations are to be performed in iterativeprocesses with assumptions for the output data.

FIGS. 2 and 3 show details of the computation steps.

FIG. 2 shows a block diagram for determination of the relative fillingper stroke (rl), based on standardized quantities for the throttle valveangle, the temperature of the intake air upstream from the throttlevalve, the mass flow through the hot film air flow meter (HFM) and therpm. A block 20 is shown for calculating the throttle valve flow rate,representing the flow equation through the throttle valve. Its inputvariables are the modeled quantity of intake manifold pressure ps, themeasured angle of the throttle valve based on its stop (wdkba), astandardized factor ftvdk, which is based on the measured temperature ofthe intake air upstream from the throttle valve, a modeled pressure(pvdk) upstream from the throttle valve and the rpm (n). At the output,the relative air mass per stroke through the throttle valve (rlroh) isobtained. This is followed by a difference forming position 21 and thenan integrator 22, both of which represent the balancing equation for thepressure in the intake manifold. At the output of integrator 22, signalps is available as an input quantity for block 20 as well as acharacteristic curve 23. Characteristic curve 23 with its relationshipbetween ps and the relative filling per stroke rl represents the suctionequation of the combustion chamber. Output signal rl is also sent todifference forming position 21.

The balancing equation in the volume upstream from the throttle valve isimplemented by a difference forming position 25 together with adownstream integrator 26. The additive input quantity of differenceforming position 25 is a signal rlhfm of the relative filling throughHFM; this signal originates from a division block 27 whose inputquantities are the HFM signal (mass flow HFM, mshfm) and an rpm signal nmultiplied by a factor KUMSRL (constant for converting from mass flow torelative air filling in the combustion chamber). The output quantity ofintegrator 26 is signal pvdk (pressure upstream from the throttle valve)which forms the corresponding input quantity of block 20.

An implementation of block 20 from FIG. 2 is shown in FIG. 3.

An input 30 for quantity wdkba is followed by a valve characteristiccurve 31 which forms a signal based on standardized angle signal wdkbaconcerning a standardized mass flow msndk through the throttle valve.This standardization also applies to an air temperature of 273° K. and apressure of 1013 hPa upstream from the throttle valve. This is followedby multiplication position 32 with additional input signal ftvdk,multiplication position 33 with signal fpvdk, and multiplicationposition 34 with the output signal of a characteristic curve 35 whoseinput quantity is the division result between modeled pressure ps andmodeled pressure pvdk (block 36). The second input signal ofmultiplication position 33 is fpvdk as the result of a division of inputquantity pvdk divided by a standard pressure of 1013 hPa (block 37).Output signal msdk (mass flow through the throttle valve) ofmultiplication position 34 subsequently undergoes division by theproduct of rpm n and factor KUMSRL in a block 38. The result of thisdivision is signal rlroh as the relative filling value through thethrottle valve.

On the basis of the physical conditions, rlhfm=rlroh=rl in steady-stateoperation, i.e., the air flow rate measured by HFM corresponds to themass flow through the throttle valve and the mass flow in the combustionchamber. In the case of non-steady-state operation, the integratorssimulating the individual air mass storages play a role.

The following equations are used in particular:

Suction equation of the internal combustion engine in general:

ma _(—) Punkt=(ps−pirg)*n*(VH/2)/(R*Ts)

where

ma_Punkt=air flow rate sucked from the combustion chamber

ps=intake manifold pressure

pirg=partial pressure caused by residual gas in the combustion chamber

n=rpm

VH=piston displacement of the engine

Ts=gas temperature in the intake manifold.

Conversion from mass flow ma_Punkt to air mass ma in the combustionchamber and division by rpm n: $\begin{matrix}{{ma} = \quad {{air}\quad {mass}\quad {in}\quad {the}\quad {combustion}\quad {chamber}}} \\{= \quad {{ma}_{-}{Punkt}\text{/}n}} \\{= \quad {\left( {{p\quad s} - {pirg}} \right)*{\left( {{VH}\text{/}2} \right)/{\left( {R*{Ts}} \right).}}}}\end{matrix}$

Standardized quantities are used for the control unit: standard air massin the combustion chamber

m _(—) norm=(Pn*VH/2)/(R*Tn).

Definition of rl as the relative air filling in the combustion chamber:$\begin{matrix}{{rl} = \quad {{{ma}/m_{-}}{norm}}} \\{= \quad {\left( {{p\quad s} - {pirg}} \right)*{{Tn}/\left( {{Pn}*{Ts}} \right)}}}\end{matrix}$

under the standard conditions: Tn=273 K, Pn=1013 hPa where$\begin{matrix}{{fupsrl} = \quad {{factor}\quad {for}\quad {converting}\quad {pressure}\quad {in}\quad {the}\quad {intake}\quad {manifold}}} \\{\quad {{into}\quad {relative}\quad {air}\quad {filling}\quad {in}\quad {the}\quad {combustion}\quad {chamber}}} \\{= \quad {{Tn}/\left( {{pn}*{Ts}} \right)}}\end{matrix}$

the suction equation is obtained in control unit quantities as

rl=(ps−pirg)*fupsrl.

Balancing equation for the filling in the intake manifold (volume 17) ingeneral (implemented by addition position 21 with a downstreamintegrator 22):

d(ms)/dt=mdk _(—) Punkt−ma _(—) Punkt.

With standardized control quantities

d(ms/m _(—) norm)/dt=(mdk _(—) Punkt−ma _(—) Punkt)/m _(—) norm

and

rl _(—) Punkt=ma _(—) Punkt/m _(—) norm

and

rlroh _(—) Punkt=mdk _(—) Punkt/m _(—) norm

it holds that:

d(ms/m _(—) norm)/dt=rlroh _(—) Punkt−rl _(—) Punkt.

The gas equation yields the relationship between air mass ms in theintake manifold and intake manifold pressure ps:

 ps*Vs=ms*R*Ts.

Solving for ms yields:

ms=(ps*Vs)/(R*Ts).

Based on a standard mass, this yields: $\begin{matrix}{{m\quad s\text{/}m_{-}{norm}} = \quad {\left( {\left( {p\quad s*{Vs}} \right)/\left( {R*{Ts}} \right)} \right)*\left( {\left( {R*{Tn}} \right)\text{/}\left( {{Pn}*{VH}\text{/}2} \right)} \right)}} \\{= \quad {\left( {p\quad s*{VS}*{Tn}} \right)\text{/}{\left( {{Pn}*{VH}\text{/}2*{Ts}} \right).}}}\end{matrix}$

Inserting this into the standardized balancing equation yields:

d*((ps*Vs*Tn)/(Pn*VH/2*Ts))/dt=(rlroh _(—) Punkt−rl _(—) Punkt).

This yields:

d*ps/dt=(rlroh _(—) Punkt−rl _(—) Punkt)*((VH/2*Ts*Pn)/(Vs*Tn)).

With

rl _(—) Punkt=rl*n

and

rlroh _(—) Punkt=rlroh*n

this yields:

d*ps/dt=((VH/2*Ts*Pn*n)/(Vs*Tn))*(rlroh−rl).

Finally, with substitution, this yields: $\begin{matrix}{{KIS} = \quad {{integration}\quad {constant}\quad {for}\quad {the}\quad {intake}\quad {manifold}\quad {model}}} \\{= \quad {\left( {{VH}\text{/}2*{Ts}*{Pn}*n} \right)\text{/}\left( {{Vs}*{Tn}} \right)}}\end{matrix}$

the control unit equation in differential form

d*ps/dt=KIS*(rlroh−rl)

and in integral form

ps=KIS*integral((rlroh−rl)*dt.

Flow rate equation for the throttle valve (block 20, individual elementsin FIG. 3) in general:

msdk(wdkba)=pvdk*(1/(R*Tvdk))**(1/2)*Adk(wdkba)*my*Xi(Ps/pvdk)*k

where

msdk: mass flow through the throttle valve

wdkba: throttle valve angle based on stop

pvdk: pressure upstream from the throttle valve

Tvdk: temperature upstream from the throttle valve

Adk: cross-section of the opening of the throttle valve

my: coefficient of friction

Xi: outflow characteristic curve.

The throttle valve is measured as a function of the throttle valve angleunder standard conditions:

msndk(wdkba)=pn*(1/(R*Tn))**(1/2)*Adk(wdk)*my*Xi(Psn/pvdk)*k.

With the following substitutions:

fpvdk=pvdk/Pn

ftvdk=(Tn/Tvdk)**(1/2)

KLAF=Xi(ps/pl)/Xi(psn/pl)

psn=standard pressure downstream from the throttle valve

the quotient msdk(wdkba)/msndk(wdkba) from the two equations yields therelationship:

msdk(wdkba)=msndk(wdkba)*ftvdk*fpvdk*KLAF.

This yields the value for rlroh at the output of division position 38from FIG. 3 as follows:

rlroh=msdk/(n* KUMSRL)

where

KUMSRL=conversion constant.

Balancing equation in volume 16 between the throttle valve and thesupercharger (addition position 25 and integrator 26 from FIG. 3) ingeneral:

d(ml)/dt=mhfm _(—) Punkt−mdk _(—) Punkt.

With standardized control quantities, this yields:

d(ml/m _(—) norm)/dt=(mhfm _(—) Punkt−mdk _(—) Punkt)/m _(—) norm

If

 rlhfm _(—) Punkt=mhfm _(—) Punkt/mnorm

and

rlroh _(—) Punkt=mdk _(—) Punkt/m _(—) norm

then it follows that:

d(ml/m _(—) norm)/dt=rlhfm _(—) Punkt−rlroh _(—) Punkt.

The relationship between air mass ml in the boost volume and boostpressure pl yields the gas equation:

pl*Vl=ml*R*Tl.

Solving for ml yields:

ml=(pl*Vl)/(R*Tl).

Based on a standard mass, this yields: $\begin{matrix}{{m\quad l\text{/}m_{-}{norm}} = \quad {\left( {\left( {{pl}*{Vl}} \right)/\left( {R*{Tl}} \right)} \right)*\left( {\left( {R*{Tn}} \right)/\left( {{Pn}*{VH}\text{/}2} \right)} \right)}} \\{= \quad {\left( {{pl}*{Vl}*{Tn}} \right)/{\left( {{Pn}*{VH}\text{/}2*{Tl}} \right).}}}\end{matrix}$

Inserting into the standardized balancing equation

d(ml/m _(—) norm)/dt=rlroh _(—) Punkt−rl _(—) Punkt

and solving for d(pl)/dt yields:

d(pl)/dt=(rlroh _(—) Punkt−rl _(—) Punkt)/(VH/2*Tl*Pn)/(Vl*Tn).

With rlhfm_punkt=rlhfm*n

and rlroh_punkt=rlroh*n

and the substitution $\begin{matrix}{{KIL} = \quad {{integration}\quad {constant}\quad {for}\quad {the}\quad {boost}\quad {volume}}} \\{= \quad {\left( {{VH}\text{/}2*{Tl}*{Pn}*n} \right)\text{/}\left( {{Vl}*{Tn}} \right)}}\end{matrix}$

this yields the control unit equation in differential form:

d(pl)/dt=KIL*(rlhfm−rlroh)

and in integral form

pl=KIL*integral(rlhfm−rlroh)*dt.

What is claimed is:
 1. A method of determining air entering cylinders ofan internal combustion engine having a supercharger, comprising thesteps of: using a suction equation to represent a first relationshipbetween a relative filling per stroke and an intake manifold pressure;using a first balancing equation for a filling in an intake manifold torepresent a second relationship between the intake manifold pressure, arelative air mass per stroke through a throttle valve, and the relativefilling per stroke; using a flow rate equation at the throttle valve torepresent a third relationship between the relative air mass per strokethrough the throttle valve, a mass flow through the throttle valve, andan rpm of the internal combustion engine; using a second balancingequation in a first volume between the throttle valve and thesupercharger to represent a fourth relationship between an air massentering the internal combustion engine, the relative air mass throughthe throttle valve, and one of a boost pressure and a pressure upstreamfrom the throttle valve; and determining the air using the suctionequation, the first balancing equation, the flow rate equation, and thesecond balancing equation, the air being determined as a function of atleast the rpm, an air throughput in the intake manifold, throttle valveposition values and temperature, the suction equation, the first andsecond balancing equations, and the flow rate equation using valuesbased on standard conditions for the equations.
 2. The method accordingto claim 1, further comprising the steps of: basing the suctionequation, the first balancing equation, the flow rate equation, and thesecond balancing equation on a two-mass storage model; forming a firstmass using a first air mass in a volume upstream from the throttlevalve; and forming a second mass using a second air mass in a volumedownstream from the throttle valve.
 3. The method according to claim 1,further comprising the step of: performing individual calculations byiterative processes with assumptions for output data.
 4. The methodaccording to claim 1, further comprising the step of: calculating athrottle valve flow rate using the flow rate equation and two modeledpressure values, the two modeled pressure values being derived from thefirst balancing equation and the second balancing equation.
 5. Themethod of claim 1, wherein the suction equation is a function of theintake manifold pressure.
 6. The method of claim 5, wherein the suctionequation is further a function of a partial pressure caused by residualgas in a combustion chamber.
 7. The method of claim 6, wherein thesuction equation is further a function of the rpm.
 8. The method ofclaim 7, wherein the suction equation is further a function of a pistondisplacement.
 9. The method of claim 1, wherein the suction equation isdefined by the equation ma_punkt=(ps−pirg)*n*(VH/2)/(R*Ts), in whichma_Punkt is an air flow rate sucked from a combustion chamber, ps is theintake manifold pressure, pirg is a partial pressure caused by residualgas in the combustion chamber, n is the rpm, VH is a pistondisplacement, and Ts is a gas temperature in the intake manifold. 10.The method of claim 1, wherein the relationship defined by the suctionequation is rl=(ps−pirg)*fupsrl, in which rl is the relative filling perstroke, ps is the intake manifold pressure, pirg is a partial pressurecaused by residual gas in a combustion chamber, and fupsrl is a factorfor converting the intake manifold pressure into the relative fillingper stroke.
 11. The method of claim 1, wherein the first balancingequation is a function of an air flow rate sucked into a combustionchamber.
 12. The method of claim 1, wherein the first balancing equationis defined by the equation d(ms)/dt=mdk_Punkt−ma_Punkt, in whichd(ms)/dt is a change in air mass with respect to time, mdk_Punkt is anair flow rate through the throttle valve, and ma_Punkt is an air flowrate sucked into a combustion chamber.
 13. The method of claim 1,wherein the relationship defined by the first balancing equation isps=KIS*integral((rlroh−rl)*dt, in which ps is the intake manifoldpressure, KIS is an integration constant, rlroh is the relative air massper stroke, and rl is the relative filling per stroke.
 14. The method ofclaim 1, wherein the flow rate equation is a function of the mass flowthrough the throttle valve.
 15. The method of claim 14, wherein the flowrate equation is further a function of a pressure upstream from thethrottle valve.
 16. The method of claim 1, wherein the flow rateequation is defined by the equationmsdk(wdkba)=pvdk*(1/(R*Tvdk))**(1/2)*Adk(wdkba)*my*Xi(Ps/pvdk)*k, inwhich msdk is the mass flow through the throttle valve, wdkba is athrottle valve angle, pvdk is a pressure upstream from the throttlevalve, Tvdk is a temperature upstream from the throttle valve, Adk iscross-section of an opening of the throttle valve, my is a coefficientof friction, and Xi is an outflow characteristic curve.
 17. The methodof claim 1, wherein the relationship defined by the flow equation isrlroh=msdk/(n*KUMSRL), in which rlroh is the relative air mass perstroke through the throttle valve, msdk is the mass flow through thethrottle valve, and KUMSRL is a conversion constant.
 18. The method ofclaim 1, wherein the second balancing equation is a function of an airflow rate through the throttle valve.
 19. The method of claim 1, whereinthe relationship defined by the second balancing equation ispl=KIL*integral(rlhfm−rlroh)*dt, in which pl is the boost pressure, KILis an integration constant, rlhfm is the air mass entering the internalcombustion engine, and rlroh is the relative air mass through thethrottle valve.